FmRα analysis: Rapid and direct estimation of relaxation and kinetic parameters from dynamic nuclear polarization time courses.

Abstract

To introduce a direct method for estimating relaxation and kinetic parameter values from rapid dissolution dynamic nuclear polarization (RD-DNP) NMR time courses. The analysis relied on a kinetic model that is often used to analyze data in these studies-a unidirectional (bio)chemical reaction with rate constant k1 , coupled to longitudinal relaxation of the magnetization of substrate and product that is characterized by the time constant T1 . The latter value was estimated from the width of the product curve (peak) at the height α relative to the maximum height. We showed α ∼ 0.8 under most conditions, so we measured the interval between the falling and rising parts of the curve at the relative height 0.8. We called this the "fall-minus-rise time at height α," or FmRα , and found that FmR0.8 ∼ T1 . The ratio β = (product signal/substrate signal) when the product is maximal was shown to be equal to k1 T1 . Therefore, k1 = β/FmR0.8 . FmRα analysis was demonstrated with (13) C NMR RD-DNP data recorded from hemolysates and from previously published data. FmRα analysis enables immediate estimates of kinetic and relaxation parameters from (13) C NMR RD-DNP data. The values can be used as initial estimates in more extensive computer-based data-regression analysis.